Biquad antenna for 2.4 GHz for stand-alone use

Radio Laboratory Handbook of the ICTP “School On Digital Radio Communications for Research and Training in Developing Countries”

This antenna is a directive one, useful for a short distance Point-to-Point
link. It may be also used as a feeder for a Parabolic Dish or Grid. It is very
cheap and quite easy to build, requiring just a piece of wire, an N socket
and a metallic plate. The plate has a hole drilled in the middle to
accommodate an N type socket. The wire is shaped as an ‘8’, but with
squared angles and then soldered to the N socket. For this antenna the
gain will be in the order of 10 to 12 dBi, with a beamwidth of around 60
degrees.

Parts list:
- one screw-on N-type female connector
- 30 cm of copper or brass wire of 2 mm of diameter
- a square metallic plate of at least 12.3x12.3 cm (aluminum is preferable)

Tools required:
- ruler
- pliers
- file for metal
- small rat-tail file
- cutter
- saw for metal
- soldering iron
- solder
- drill with a set of bits for metal (with a 1.5 cm diameter bit)
- vice or clamp
- hammer
- spanner or monkey wrench

Construction:

1. Straighten the wire using the vice.
2. Cut the metallic plate to have a square shape of 12.3x12.3 cm. To do
   this, you may use the saw, but we suggest to use a thin (0.8 to 1.5 mm)
   aluminum plate, which can be cut with a cutter. Draw the correct
   dimensions on both sides of the plate with a marker. Carve the drawn lines
   with the cutter pressing firmly, helping yourself with the ruler. Do this a
   couple of times, on both sides of the plate. Bend the plate over the lines
   until it breaks.
3. The edges can be now very sharp. Be careful when handling the
   plate. Use the file to smooth the edges all around.
4. With a marker and a ruler, draw the diagonals on the metallic plate,
   finding its center. With a small diameter drill bit, make a hole at the
   center of the plate. Increase the diameter of the hole using bits with an
   increasing diameter.(The hole should fit exactly the N connector. Use the file if needed).
5. Now we want to shape the wire as an ‘8’, composed by two squares
   connected on one edge. The two squares have a side of 3.05 cm. Bend the wire at 90 degrees in his central point using the vice and the hammer.
6. With a marker, draw a line at 3.05 cm from the edge, and bend the
   wire at 90 degrees in this point with the vice and the hammer as before,
   but in the opposite direction (it should look like a ‘Z’).
   
7. Draw another line at 3.05 cm from this new edge, and bend the wire
   at 90 degrees in this point, in the same direction as before.
8. Draw now a line at 3.05 cm from the last edge, and a second line
   after 2.3 cm from the first one.
9. Bend the wire at 90 degrees in the second
   line, in a direction orthogonal to the plane containing the wire.
10. Shape the second half of the wire to obtain another square,
    repeating the procedure described in steps from 6 to 9
11. With the saw and the rat-tail file make two small, half-round shaped
    cuts in the connector’s nut at 60 degrees one from each other. The cuts
    should be on two contiguous edges of the nut, and should be large enough
    to fit half of the wire’s diameter. File also around the cuts (Be careful not to cut too deeply inside the nut: enough metal should remain to ensure its robustness.)
    
12. Trim the two ends of the wire at a length of 1.5 cm.
    
13. The wires should now fit in the nut’s cuts
14. Tin the ends of the wire for 0.5 cm. Tin around and inside the cuts
    of the nut with a small amount of solder, and then solder the wires to the
    nut.
15. Remove the exceeding solder with the file, so that the nut can be
    screwed correctly
16. Insert the connector into the hole of the metallic plate and screw
    the nut with the wire soldered on it.
17. We now want to solder the central pin of the connector to the
    center of the shaped wire. You may have either a short or long type of N
    connector (The central pin of the long type may be soldered directly on the shaped
    wire, while the short type of connector needs ad additional short piece of
    straight wire to be soldered into the central pin)
18. Tin the central pin of the connector and solder the center of the
    shaped wire to it
19. The antenna is now completed. If you have a Spectrum Analyzer
    with Tracking Generator and a Directional Coupler, you can check the
    curve of the reflected power of the antenna.
    
    
    

Quarter wave omnidirectional antenna for 2.4 GHz

Radio Laboratory Handbook
of the ICTP “School On Digital Radio Communications for Research and Training in Developing Countries”
( Marco Zennaro & Carlo Fonda )

This is a simple and cheap omnidirectional antenna good for surveying signal strength using wlan tools. It is built using an N-type female chassis mount connector and five short lengths of copper or brass wire. The driven element is the wire soldered into the central conductor of the connector, with a length of one quarter wavelength. The four radials are also one quarter wavelength long, and are soldered into each corner hole of the connector. Each groundplane is cut to length and then bent over at 30 degrees from the horizontal to attempt to match the impedance to 50 Ohms. The gain of this antenna will be between 3 dBi and 4 dBi depending on final tuning.

Parts list:

• one N-type chassis mount female connector with four-holes flange (good quality one with teflon insulator is recommended)
• 20 cm of copper or brass wire of 2 mm of diameter

Tools required:

• ruler and goniometer
• pliers
• a file for metal
• a small rat-tail file for metal
• one powerful soldering iron of about 80 -100 W
• one soldering iron
• solder
• vice
• hammer

Construction

1. With the pliers, cut the wire in 5 pieces of 4 cm each.
2. File the flange of the connector near the holes in order to remove the plated surface. Use the rat-tail file to do the same on the internal part of the holes. This is done to prepare the surface of the connector for tinning.
3. Power on the high power soldering iron and let it heat for a couple of minutes. Apply the soldering iron to the connector until it gets hot (really hot! Be very careful!), but avoid melting the dielectric. Then tin the area around and inside the holes by applying solder until it flows. Avoid filling the holes with solder. Tinning is required to facilitate the process of soldering the wires to the connector.
4. Smooth with the file one side of each of the wires. Tin the wires for around 1 cm at the smoothed end, using the high power soldering iron.
5. Bend at 90 degrees 0.5 cm of the tinned side of the wires with the pliers. Do it for four of the wires, leaving one straight. Help yourself with the vice and the hammer.
6. Place firmly the connector in the vice, avoiding damaging the screw. Place the tinned bend side of one wire in a hole of the flange. Keeping it with the pliers, position the wire horizontally and along the direction of the diagonal. Apply the high power soldering iron shortly to the connector and with a small amount of solder, solder the wire to the connector. Avoid melting the dielectric of the connector. You may find useful getting somebody else keeping the wires in place with the pliers while you are soldering.
7. With the low power soldering iron, tin the central pin of the connector. Keeping the straight wire vertical with the pliers, solder its tinned side in the hole of the central pin.
8. Trim the exceeding part of the wires under the flange.
9. With the pliers, bent over the four radials at 30 degrees from the horizontal plane. This is done to match the impedance to 50 Ohms. To facilitate this operation, you may draw the 30 degrees angle on paper, and compare the antenna with it as shown.
10. Trim the radial at a length of 3,05 cm measured from the corner of the flange. Smooth the end of the wires with the file.
11. Trim the central wire at 3.05 cm measured from the flange surface. If you have a Spectrum Analyzer with Tracking Generator and a Directional Coupler, you can leave the central wire 0.5 cm longer and check the curve of the reflected power of the antenna. Trimming the wire at steps of 0.1 cm or less, you can tune the antenna to have the minimum reflected power at a frequency of 2.44 GHz. The pictures below show the display of the Spectrum Analyzer at the beginning and at the end of the tuning procedure. A difference of a few millimeters changes the frequency of resonance of the antenna of some hundred MHz. You are done!